1. Field of the Invention
The present invention relates to a semiconductor package which can be readily mounted on a flexible circuit board which can be bent, and a production method thereof.
2. Description of the Related Art
Recently, since electronic devices have been becoming lighter, thinner and smaller, a demand for a small and light semiconductor device for mounting on such an electronic device is increasing. For satisfying such a demand, a miniaturized semiconductor package such as a BGA (Ball Grid Array) type or CSP (Chip Scale Package) type semiconductor package has been widely used. As used herein, a semiconductor package refers to a semiconductor chip with active elements such as diodes and transistors, and circuitry such as electrodes and wiring formed on a surface, and the surface being molded with a resin or covered with a resin layer.
FIG. 6A is a cross-sectional view showing an exemplary semiconductor package of a conventional QFP (QuadFlatPackage)type. In such a semiconductor package, a semiconductor chip 22 is mounted on a die pad 30 with a die bond adhesive 25 provided therebetween. The die pad 30 and a package lead 27 form a part of a lead frame. The package lead 27 is connected via wire 23 to an electrode (not shown) provided on a surface of the semiconductor chip 22 on which circuits are formed. The semiconductor chip 22, the die pad 30, and the package lead 27 are molded with a resin 21. For mounting this QFP type semiconductor package on a circuit board, the package lead 27 which serves as an external connection terminal is soldered onto the circuit board so as to electrically connect the semiconductor package and the circuit board.
FIG. 6B is a diagram showing an exemplary semiconductor package of a conventional CSP (or BGA) type. In such a semiconductor package, a semiconductor chip 22 is adhered onto circuit pattern 26 by using an adhesive film or a paste of a die bond adhesive 25. The circuit pattern 26 is provided on an interposer substrate 28 and connected via wire 23 to an electrode (not shown) provided on a surface of the semiconductor chip 22 on which circuits are formed. Further, the circuit pattern 26 is connected to a solder ball 24 through a penetrate hole 29 provided in the interposer substrate 28. In order to protect the semiconductor chip 22 and the wire 23, a surface of the interposer substrate 28 on which the semiconductor chip 22 is mounted is molded with a resin 21. For mounting this CSP type semiconductor package on a circuit board, the solder ball 24 is melted and soldered onto the circuit board so as to electrically connect the semiconductor package and the circuit board. Although the size of the semiconductor package is slightly larger than the size of the semiconductor chip, this CSP type semiconductor package is much smaller and lighter than the conventional QFP type semiconductor package.
A semiconductor package which allows a further miniaturization is disclosed in Japanese Laid-Open Publication No. 61-50344. As shown in FIG. 6C, such a semiconductor package comprises a conductive adhesive resin layer 32 and a semiconductor chip 22 which have the same size, and the conductive adhesive resin layer 32 is provided on a surface of the semiconductor chip 22 on which electrodes 31 are provided.
Recently, as electronic devices are becoming smaller, the thicknesses of circuit boards have been reduced. For placing components in a small and complicated-shape space inside a small portable device with high density, a Flexible Printed Circuit (FPC) which can be freely bent is becoming more popular. Another method which has been proposed for producing a small and light device is to pattern circuits directly onto a housing forming an electronic device.
In such a circumstance, the conventional semiconductor packages described above have the following problem. Even if a thin substrate or a flexible circuit board can be bent (deformed) into a complicated shape in a small portable device, a semiconductor package is rigid and unbendable. Therefore, the semiconductor package which cannot be deformed mounted on the flexible circuit board which can be freely bent, prevents the circuit board from being accommodated in a small and complicated-shape space inside a small portable device. Furthermore, it is difficult to mount the rigid and unbendable semiconductor package on circuits formed on a curved surface of a housing.
The above described problem is troublesome particularly when accommodating a circuit board on which a large semiconductor package is mounted in a small portable device. The large semiconductor package can be either a large-size semiconductor package which accommodates a semiconductor chip which is increased in size as a circuit scale and a memory capacity mounted on an electronic device increase, or a multi-chip package which accommodate a plurality of semiconductor chips within a single package. Specifically, mounting the semiconductor package onto the circuit board affects a deformation, and bending property of the flexible circuit board. Thus, the circuit board on which the semiconductor package is mounted cannot be accommodated in the small portable device by making use of the properties of the flexible circuit board that can freely deform and bend. Accordingly, the conventional semiconductor package may prevent an implementation of mounting of components with high-density and miniaturization of the devices.
Furthermore, as the portable devices become smaller, and as electronic components comprised in the portable devices use much higher frequencies, problems such as interactions among electronic components including semiconductor chips during an operation, electromagnetic wave disturbances, electromagnetic wave noise, and the like are less likely to occur. Particularly, a thin semiconductor package is susceptible to electromagnetic wave noise. Therefore, a serious problem may occur in the miniaturized portable device.